REPORT OF COMMITTEE ox PUBLICATION 151 



.METHODS OF PREPARATION AND RELATIVE VALUE OF 

 BORDEAUX MIXTURES. 



By O. BUTLER, Ph. D., 

 Botanist, New Hampshire Agricultural Experiment Station. 



I. 



Anyone who has perused the literature relating to the copper fungicides 

 cannot but have felt some surprise at the multiplicity of formulae given for 

 the preparation of either Bordeaux mixture of Dauphiny mixture, for instance 

 and at the lack of sufficient ground for this multiplicity. We are, of course, 

 informed by the author of every variant that his formula fulfills certain 

 requirements that justify its publication, though no attempt is usually made 

 to prove the validity of the contention. The characters that a copper fungi- 

 cide must possess are, however, easily defined; and no formula should be 

 published unless it can be shown to possess in a degree not hithertofore 

 obtained, the essential qualities demanded. I have said that the characters 

 that a copper fungicide must possess are readily defined. They are: 



1. The wash must not be toxic to the plant it is destined to protect. 



2. The active principle must be efficient, that is, the unit copper must 

 have a high fungicidal value. 



3. The active principle must be effective, that is, the unit copper must 

 have a high protective value. 



4. The active principle must be adhesive. 



5. The active principle must dissolve sufficiently rapidly under the 

 action of the weather to be efficient. 



While the literature does not yet afford complete information regarding 

 the manner in which the various copper fungicides meet the five essentials 

 above mentioned, our knowledge has grown sufficiently during the last few 

 years to warrant a brief study of one important fungicide currently used in 

 viticulture, to wit, Bordeaux mixture. 



II. 



The Bordeaux mixtures used in practice are reducible, as I have pointed 

 out elsewhere,! to three types depending on the ratio cupric sulphate to 

 calcic oxide used in their preparation, which three types may be character- 

 ized as follows: 



1. Neutral Bordeaux mixtures. 



2. Slightly alkaline Bordeaux mixtures. 



3. Strongly alkaline or basic Bordeaux mixtures. 



The neutral Bordeaux mixtures are washes in which the ratio cupric 

 sulphate to calcic oxide is 1:0.2 (Woburn Bordeaux mixture) or approxi- 

 mately 1:0.2 ("acid" Borbeaux mixture). In the former case the copper is 



i Butler. O. Bordeaux Mixture: I Physico-chemical studies, Phytopath- 

 ology 4:125-180, 1914. 



